In general, an electric pole has a cylindrical shape having a slow gradient, and is manufactured to have various length of 7 to 17 m. One end of the electric pole, which is buried under the ground, is called as a proximal end, while the other end is called as a distal end. The electric pole is mainly composed of concrete, and a frame consisting of tensile cores arranged in a longitudinal direction of the electric pole and iron wires wound around and attached to the circumferences of the tensile cores further is incorporated into the electric pole to increase the strength thereof.
FIG. 1 is a cross sectional view illustrating the construction of a conventional apparatus of manufacturing an electric pole, and FIGS. 2 and 3 are view illustrating a coupling structure of a tensile core applied to the conventional apparatus.
Referring to FIG. 1, the conventional apparatus of manufacturing the electric pole has a structure capable of being divided a mold 20 into an opened mold and a closed mold.
The mold 20 includes a proximal end plate 30 mounted to one end thereof for forming a proximal end 12, a proximal end tensile plate 32 spaced from the proximal end plate 30 at a constant spacing, and a proximal end tensile core fixing plate 34 having a tensile core 64 with one side penetrating through a bottom surface of the proximal end tensile plate 32.
The mold 20 further includes a distal end plate 40 mounted on one end thereof for forming a distal end 14, a distal end tensile plate 42 spaced from the distal end plate 40 at a constant spacing and coupled to a tension shaft 50, and a distal end tensile core fixing plate 44 having the tensile core 64 with the other side penetrating through an upper surface of the distal end tensile plate 32. The tension shaft 50 is rotatably engaged to an exterior tension through a bolt type, with the tensile shaft penetrating through a butt-end plate 46, and is fastened by a nut 52.
The distal end plate 40, distal end tensile plate 42, proximal end plate 30, and proximal end tensile plate 32 form a hole, through which both sides of the tensile cores 64, arranged in a circle shape, extend.
The mold 20 is provided on its outer circumference with a plurality of rings (not shown) which are contacted with a rotary roller and receive rotary power from the rotary roller.
The proximal end tensile core fixing plate 34 and the distal end tensile core fixing plate 44 are formed with a number of fastening holes 36 of a peanut shape so as to have a supporting force in a stage that the tensile cores 64 penetrate through the fixing plates 34 and 44, as shown in FIGS. 2 and 3. The fastening hole 36 has a large-diameter portion 37 and a small-diameter portion 38.
The tensile core 64 has a head 66 so that both ends are inserted into the large-diameter portion 37 and the tensile core is engaged by the fixing plate 34 by the head 66.
The operation of the conventional mold will now be described.
First Process
A plurality of tensile cores 64 are cut to have a length of 400 to 500 mm longer than that of the electric pole 10, and then are arranged along a longitudinal direction of the electric pole. Slender iron wires are wound and welded around the surroundings of the tensile cores 64 to form a frame. Both ends of the tensile core 64, arranged in a longitudinal direction in the frame, are headed and pressurized to form the head 66.
Second Process
A release agent is applied on the mold 20, and the both sides of the tensile core 64 penetrate through the distal end plate 40, distal end tensile plate 42, proximal end plate 30, and distal end tensile core 32, so that the head 66 of the tensile core 64 is engaged by the fastening hole 36 of the proximal end tensile core fixing plate 34 and the distal end tensile core fixing plate 44. Then, the frame prepared in the first process is seated on an opened mold 20.
Third Process
In order to prevent the deformation of the entire mold when inputting the concrete into the mold 20, the tensile core 64 is strained by the tensioner. After that, the mold 20 is rotated while the mold is closed, by a centrifuge to form a hollow of a thickness corresponding to that of the defined electric pole 10.
At that time, the tensile core 64 is provided with tension sufficient for maintaining a straight line relative to the tension shaft 50. It is noted that if the tensile core 64 is pulled, the tensile core is stretched, so that the head 66 and a portion adjacent to the small-diameter portion 38 soften to release the tension state.
Fourth Process
The concrete of the electric pole 10 is treated through a steam cure using a boiler to have a desired strength.
Fifth Process
After tensile cores 64 extend between the distal end plate 40 and the distal end tensile plate 42 and proximal end plate 30 and proximal end tensile plate 32 are cut using a welding rod, the electric pole 10 is transferred, and then a fine cut of the tensile cores 64 remaining at the proximal end 12 and distal end 14 and the natural cure is performed to complete the electric pole 10.
With the construction of the conventional electric pole manufacturing apparatus, there is a problem in that the tensile cores 64 are cut to have a length of about 400 to 500 mm longer than that of the electric pole 10 to stretch the tensile plate 64, thereby increasing the cost by providing a surplus length of the tensile core 64.
There is another problem in that the head 66 of the tensile core 64 is inserted into the large-diameter portion 37 of the fastening hole 36, and is moved to the small-diameter portion 38, so that the head is supported by the portion adjacent to the small-diameter portion 38 and the large-diameter portion 37 isopen, thereby causing the shape of the distal end 14 of the electric pole to be poor.
Specifically, after the head 66 of the tensile core 64 is passed through the large-diameter portion 37 of the fastening hole 36 formed in the distal end tensile core fixing plate 44, the head 66 reaches the small-diameter portion 38 by slightly rotating the fixing plate 44. The head is engaged by the portion adjacent to the small-diameter portion 38, thereby restraining the tensile plate 64.
With this construction when the large-diameter portion 37 opens, since the concrete or moisture of the electric pole 10 leaks through the clearance, the shape of the distal end 14 of the electric pole is caused to be poor.
In order to address the problem, in case of closing the exposed large-diameter portion with a separate member, the process is more complicated.
The tensile core 64 is stretched with the construction of the fastening hole 36 constraining the tensile core 64, in which the large-diameter portion 37 communicates with the small-diameter portion 38. The distal end tensile core fixing plate 44 may move based on the tensile plate 64, and the shape of the distal end 14 of the electric pole becomes poor.
There is a further problem in that if a design load of the electric pole 10 is increased, it is impossible to arrange the tensile core 64 at the distal end 14 of a small diameter relative to that of the proximal end 12 of the electric pole 10.
Specifically, if a length of the electric pole 10 is 16 m, a design load of the electric pole is 1300 kg, and a diameter of the distal end 14 is 220 mm, twelve tensile cores 64 having a diameter of 14 mm are required. At that time, a spacing of the tensile cores 64 is 40.58 mm.
The fastening hole 36 formed in the distal end tensile core fixing plate 44 has the large-diameter portion 37 and the small-diameter portion 38. It is difficult to ensure an area forming twelve fastening holes 36 for arranging 12 tensile cores 64, so that a angle between the large-diameter portion 37 and the small-diameter portion 38 from a center axis of the distal end tensile core fixing plate 44 may satisfy the design value. Therefore, it is impossible to manufacture the electric pole 10 according to the design load.